1. Field of the Invention
The present invention generally relates to a semiconductor integrated circuit and a data storing method thereof, and specifically relates to technology that enhances secrecy of data stored in a memory device, and enhances reliability of memory operations.
2. Description of the Related Art
In recent years, information technology has progressed rapidly. Versatile information is stored as electronic data and can be accessed. With such a background, a risk is that the data written in the memory device are acquired and analyzed by an unauthorized party, and once the data are acquired, great damages are likely to be caused.
Quantity of the semiconductor memory devices used has been growing rapidly, and applications have been highly diversified. It is becoming impossible to simply replace memory device (module etc.) if a memory device is damaged during use. It is desirable that a self-repair function is provided to the memory device, such that unavailability of a system can be minimized by the self-repair function.
In a conventional manner of data writing to a semiconductor memory device, data with a low degree of secrecy are written as they are, while data with a high degree of secrecy are first encrypted by application software, and then written.
When strong code intensity, i.e., a firm protection is desired, software encryption requires a great amount of calculations, causing a response speed to be slow. Thus, protection strength has been restricted. Further, if encrypted data were read indirectly by a data pattern analyzing technique, modified, and rewritten to the memory, the encryption does not serve the purpose of storing the data intact.